The present invention generally relates to the detection of gram positive microbial contaminants. More specifically, the present invention relates to methods and compositions that employ modified bioburden testing and the detection of peptidoglycan in peritoneal dialysis solutions. Peptidoglycans are major cell wall components of gram positive organisms and thus serve as a good marker of these microbes.
Due to disease or insult or other causes, the renal system can fail. In renal failure of any cause, there are several physiological derangements. The balance of water, minerals (e.g., Na, K, Cl, Ca, P, Mg, SO4) and the excretion of a daily metabolic load of fixed ions is no longer possible in renal failure. During renal failure, toxic end products of nitrogen metabolism (e.g., urea, creatinine, uric acid, and the like) can accumulate in blood and tissues.
Dialysis processes have been devised for the separation of elements in a solution by diffusion across a semi-permeable membrane (diffusive solute transport) across a concentration gradient. Examples of dialysis processes include hemodialysis, peritoneal dialysis and hemofiltration.
Hemodialysis treatment utilizes the patient's blood to remove waste, toxins, and excess water from the patient. The patient is connected to a hemodialysis machine and the patient's blood is pumped through the machine. Catheters or the like are inserted into the patient's veins and arteries to connect the blood flow to and from the hemodialysis machine. Waste, toxins, and excess water are removed from the patient's blood and the blood is infused back into the patient. Hemodialysis treatments can last several hours and are generally performed in a treatment center about three or four times per week.
To overcome the disadvantages often associated with classical hemodialysis, other techniques were developed, such as peritoneal dialysis. Peritoneal dialysis utilizes the patient's own peritoneum as a semipermeable membrane. The peritoneum is the membranous lining of the body cavity that, due to the large number of blood vessels and capillaries, is capable of acting as a natural semipermeable membrane.
In peritoneal dialysis, a sterile dialysis solution is introduced into the peritoneal cavity utilizing a catheter or the like. After a sufficient period of time, an exchange of solutes between the dialysate and the blood is achieved. Fluid removal is achieved by providing a suitable osmotic gradient from the blood to the dialysate to permit water outflow from the blood. This allows a proper acid-base, electrolyte and fluid balance to be returned to the blood. The dialysis solution is simply drained from the body cavity through the catheter. Examples of different types of peritoneal dialysis include continuous ambulatory peritoneal dialysis, automated peritoneal dialysis and continuous flow peritoneal dialysis.
Standard peritoneal dialysis solutions contain dextrose to effect transport of water and metabolic waste products across the peritoneum. Although dextrose has the advantage of being relatively safe and inexpensive, it has a number of disadvantages. Because of the small size, dextrose is rapidly transported through the peritoneum, thus leading to the loss of osmotic gradient and loss of ultrafiltration within about 2 to 4 hours of infusion. It has been suggested that the ultrafiltration characteristics of peritoneal dialysis solutions could be improved by replacing dextrose with large molecular weight substances, such as glucose polymers. An example of a novel high molecular weight agent is icodextrin. Dialysis solutions containing icodextrin are commercially available and have been found to be useful in treating patients with end stage renal disease.
Peritonitis is a major complication of peritoneal dialysis. Clinical suspicion of peritonitis is prompted by the development of a cloudy-appearing dialysate in combination with variable clinical manifestations that may include abdominal pain, nausea, vomiting, diarrhea and fever. See, for example, Vas S I: Peritonitis. In: Nolph K D, ed. Peritoneal Dialysis. 3rd ed. Dordrecht, The Netherlands: Kluwer Academic Publishers, 1989:261–84. Most episodes of peritonitis are caused by intraperitoneal bacterial infections, and the diagnosis is usually readily established by positive dialysate cultures. However, there are several well documented causes of non-infectious or sterile peritonitis. Aseptic or sterile peritonitis, which also is described as aseptic, chemical, or culture-negative peritonitis, is typically caused by a chemical or a foreign body irritant.
One of the major outbreaks of sterile peritonitis among patients on peritoneal dialysis occurred in 1977. This was attributed to intrinsic and occult endotoxin contamination of dialysis solution. Suspected provocative batches of peritoneal dialysate had endotoxin levels in the range of 2 to 2.5 endotoxin units (EU)/mL. See, for example, Karanicolas S, Oreopoulos D G, Izatt S H, et al: Epidemic of aseptic peritonitis caused by endotoxin during chronic peritoneal dialysis, N Engl J Med 1977; 296:1336–7. A similar epidemic of aseptic peritonitis caused by endotoxin contamination in continuous cycling peritoneal dialysis patients was reported in 1998. See, for example, Mangram A J, Archbald L K, Hupert M, et al: Outbreak of sterile peritonitis among continuous cycling peritoneal dialysis patients, Kidney Int 1988; 54:1367–71. Other reported causes of aseptic peritonitis include intraperitoneal administered vancomycin (See, for example, Smith T, Baile G, Eisele G: Chemical peritonitis associated with intraperitoneal vancomycin, Ann Pharm 1991; 25:602–3, and Chancy D I, Gouse SF: Chemical peritonitis secondary to intraperitoneal vancomycin, Am J Kidney Dis 1991; 17:76–9), amphotericin B (See, for example, Benevent D, El Akoun N, Lagarde C: Dangers of administration of intraperitoneal amphotericin B in continuous ambulatory peritoneal dialysis, Press Med 1984; 13:1844), and acetaldehyde (See, for example, Tuncer M, Sarikaya M, Sezer T, et al: Chemical peritonitis associated with high dialysate acetaldehyde concentrations, Nephrol Dial Transplant 2000; 15:2037–40). A unique form of aseptic peritonitis, eosinophilic peritonitis, is a much more common entity that can occur shortly after the start of peritoneal dialysis. See, for example, Gokal R, Ramos J M, Ward M K, et al: ‘Eosinophilic peritonitis’ in CAPD, Clin Nephrol 1981; 15:328–330.
As previously discussed, glucose polymers, such as icodextrin, can be used in place of dextrose in peritoneal dialysis solutions. Icodextrin is a polymer of glucose derived from the hydrolysis of corn starch. It has a molecular weight of 12–20,000 Daltons. Peritoneal dialysis solutions containing icodextrin as the osmotic agent are, in general, used for long dwell (>4 hour) exchanges. The majority of glucose molecules in icodextrin are linearly linked with a (1–4) glucosidic bonds (>90%) while a small fraction (<10%) is linked by a (1–6) bonds.
Icodextrin was introduced into clinical practice in the United Kingdom in 1994 and in other European countries beginning in 1996. The clinical advantages of icodextrin for long dwells, especially in patients with high and high average transport status and loss of ultrafiltration, is well-accepted and contributed to its global popularity. See, for example, Wilkie M E, Plant M J, Edwards L, et al: Icodextrin 7.5% dialysate solution (glucose polymer) in patients with ultrafiltration failure: extension of technique survival, Perit Dial Int 1997; 17:84–7; Wolfson M, Piraino B, Hamburger R J, Morton A R, for the Icodextrin Study Group: A randomized controlled trial to evaluate the efficacy and safety of icodextrin in peritoneal dialysis, Am J Kidney Dis 2002; 40:1055–65; and Mujais S, Nolph K, Gokal R, et al: Evaluation and management of ultrafiltration problems in peritoneal dialysis, Perit Dial Int 2000; 20(Suppl 4):S5–S21.
Since the introduction of icodextrin for use in peritoneal dialysis solutions, sporadic cases of aseptic peritonitis have been reported. See, for example, Pinerolo M C, Porri M T, D'Amico G: Recurrent sterile peritonitis at onset of treatment with icodextrin, Perit Dial Int 1999; 19:491–2; Williams P: Timely initiation of dialysis. Am J Kidney Dis 34:594–595, 1999; Williams P F, Foggensteiner L: Sterile/allergic peritonitis with icodextrin in CAPD patients, Perit Dial Int 2002; 22:89–90; Foggensteiner L, Bayliss J, Moss H, et al: Timely initiation of dialysis—single-exchange experiences in 39 patients starting peritoneal dialysis, Perit Dial Int 2002; 22:471–6; Heering P, Brause M, Plum J, et al: Peritoneal reaction to icodextrin in a female patient on CAPD. Perit Dial Int 2001; 21:321–2; Del Rosso G, Di Liberato L, Pirilli A, et al: A new form of acute adverse reaction to icodextrin in peritoneal dialysis patient, Nephrol Dial Transplant 2000; 15:927–8; Goffin E, Scheiff J M: Transient sterile chemical peritonitis in a CAPD patient using icodextrin, Perit Dial Int 2002; 22:90–1; Tintillier M, Pochet J M, Christophe J L, Scheiff J M, et al: Transient sterile chemical peritonitis with icodextrin: clinical presentation, prevalence, and literature review, Perit Dial Int 2002; 22:534–7; and Gokal R: Icodextrin-associated sterile peritonitis, Perit Dial Int 2002; 22:445–8. These patients typically presented with cloudy dialysate, no abdominal pain, and dialysate cell counts varying from 300 to 3500/mm3, with variable percentages of neutrophils, lymphocytes, and macrophages. In general, there is no change in ultrafiltration profile or peritoneal permeability for solutes. Cultures were invariably negative with no evidence of peritoneal or peripheral blood eosinophilia. Moreover, all solution components and endotoxin levels fell within the product specifications, and the icodextrin-based peritoneal dialysis solutions met all current Pharmacopoeia standards. Prompted by these reports, in 2001, the manufacturer of the icodextrin-containing solution (BAXTER HEALTHCARE CORPORATION) modified the Summary of Product Characteristics (SPC) to include cloudy effluent as an “undesirable side effect” of icodextrin. Relying on information from a global pharmacovigilence program, a greater than 10× increase in the reported cases of aseptic peritonitis associated with icodextrin was noted in 2002. A voluntary worldwide recall of several hundred batches of newly manufactured and/or released icodextrin-containing dialysis solution was prompted.
Parenteral pharmaceutical products are required to be free of contaminating substances, such as substances that can cause fever. Because endotoxins derived from gram-negative bacteria are the most common contaminant in parenteral products, the historic pyrogens of concern are LPS. Current Pharmacopeia standards are that one of two tests for pyrogenic contamination is applied to parenteral products. These tests are the rabbit pyrogen test and the LAL assay. Although generally reliable, both tests have shortcomings. The rabbit test relies on a febrile response that in turn depends upon the elaboration of pyrogenic cytokines. The rabbit pyrogen testing may be falsely negative, if the pyrogen is at a concentration too low to induce a systemic response, but of sufficient magnitude to produce a local inflammatory reaction. In turn, the more sensitive LAL test does not detect pyrogens other than LPS. Pyrogens, like viruses, fungi, DNA, gram-positive exotoxins, or bacterial cell wall components from gram positive bacteria, such as peptidoglycan and the like, will not be detected by the LAL test. See, for example, Dinarello C A, O'Conner J V, LoPreste G: Human leukocyte pyrogen test for detection of pyrogenic material in growth hormone produced by recombinant Escherichia coli, J Clin Microbiol 1984; 20:323–9; Poole S, Thorpe R, Meager A, et al: Detection of pyrogen by cytokine release, Lancet 1988; 1(8577):130; Ray A, Redhead K, Selkirk S, et al: Variability in LPS composition, antigenicity and reactogenicity of phase variants of Bordetella pertussis, FEMS Microbiol Lett 1991; 63:211–7; Taktak Y S, Selkirk S, Bristow A F, et al: Assay of pyrogens by interleukin-6 release from monocytic cell lines, J Pharm Pharmacol 1991; 43:578–82; and Fennrich S, Fischer M, Hartung T, et al: Detection of endotoxins and other pyrogens using human whole blood, Dev Biol Stand 1999; 101:131–9.
The global outbreak of aseptic peritonitis observed with icodextrin-based peritoneal dialysis solutions as discussed above serves as a sentinel example of how contemporary parenteral products with microbial, non-endotoxin contaminants may be considered safe under Pharmacopoeia standards but provoke adverse clinical effects. Therefore, a need exists to provide improved standards for parenteral products that employ detection procedures to better ensure that the parenteral products are effectively free of contaminating substances.